This invention relates to fuel injectors, more particularly, a modified pump follower for use in retarding injection timing of EMD-type unit injectors in diesel engines.
EMD-type unit injectors are injectors that feature mechanical unit injectors (as opposed to electronic control) and are widely used in the diesel engine industry, including the locomotive industry. However, with the increase of concern of harmful emissions from diesel engines and overall energy conservation, modifications to EMD-type unit injectors have become necessary so as to be more environmental friendly.
Although the prevalence of photochemical smog in metropolitan areas spurred the first public interest in reducing noxious emissions from exhaust emissions, reducing output of all types of harmful emissions, including carbon monoxide (CO), hydrocarbons (HC) and nitrous oxides (NOx) has become one of the goals of the diesel engine industry. Through the years, the diesel engine industry has greatly reduced the smoke, carbon monoxide and hydrocarbons emitted into the atmosphere. However, it is the nitrous oxides and particulate emissions that remain one of the plaguing problems for diesel engines.
In order to reduce the amount of nitrogen oxides emitted, the injector should create less heat in the combustion chamber. One method to create less heat, and thereby produce less nitrogen oxides, is by retarding the injection timing of the fuel injectors. By retarding the timing of diesel fuel injections, the combustion process occurs at a later time in the power stroke. By retarding the timing, the combustion temperature and pressure are lowered, thereby causing less nitrogen oxides to form. The amount of nitrogen oxide lessens with higher levels of retard.
The drive linkage (which includes the associated engine cam, a rocker arm assembly, a socket pad on the head of the adjusting screw and a spring-loaded tappet or follower carried by the injector pad and slidably engaged by the pad) powers the injector pump to actuate the injector plunger as determined by the engine cam profile. One possible method for retarding timing is by adjusting the screw on the output end of the engine rocker arm. As the adjusting screw is turned, the free length of the adjusting screw below the output end of the rocker arm is changed and creates a new set screw set point. As a result, the drive linkage is either shortened or lengthened until there is a predetermine specified timing distance between the top face of the follower and a fixed surface, namely the top flat face of the injector body. The specified timing distance is the distance that is obtained when the port closure of the helix of the plunger is above the point at which it will close off its associated spill port in the plunger bushing to thereby initiate injection, which is known as its set point. The set point is usually listed on the engine manufacturer's data plate. If the set point listed on the data plate does not match with the set point for the now retarded injector, a new setting gauge and new engine marking must be provided.
In addition, the new timing distance specification or adjusting screw set point prescribed to retard injection timing may vary from engine model to engine model. This variation creates a potential for human error wherein a mechanic must use multiple gages to set multiple engines.
Thus, a need exists for methods of retarding injection timing of mechanical unit injectors that are simple and minimizes human error in reducing undesirable emissions.
The relevant prior art includes the following references:
Patent No.(U.S. unless stated otherwise)InventorIssue/Publication Date6,321,723Merkle et al.Nov. 27, 20016,763,810JonesJul. 20, 20043,982,693HulsingSep. 28, 19764,984,738WinquistJan. 15, 19914,317,541BeardmoreMar. 02, 19824,054,248BeardmoreOct. 18, 19772,898,051TeichertAug. 04, 19594,213,564HulsingJul. 22, 19805,328,094Goetzke et al.Jul. 12, 19946,439,204DuquetteAug. 27, 2002